1. Field of Technology
Embodiments disclosed herein relate generally to LED operation and more specifically to filter bandwidth adjustment in a multi-loop LED dimmer control circuit.
2. Description of the Related Arts
Dimmable LED drivers generally perform two functions: regulating the LED load current based on a dimmer signal describing a level of LED brightness, and providing a constant load current if the dimmer signal describes a maximum level of brightness. In one implementation, a dimmer signal can directly modify a reference current in an LED load current control loop such that the load current varies with changes in the dimmer signal. However, in order to maintain stability in such an implementation, the bandwidth in the LED load current control loop is limited. As a result, the dimming response can be sluggish, for instance upon a rapid dimmer level adjustment.
To improve dimming response performance, the dimmer signal can instead influence a pulse-width-modulation (“PWM”) generator configured to drive an LED power circuit. In such an embodiment, a current reference signal can be used to drive the power circuit when the dimmer signal describes a maximum level of brightness. Switching between driving the power circuit based on the dimmer signal and the current reference can also be sluggish, and may result in overshoot or undershoot of LED load current provided by the power circuit. While the power circuit will correct the load current overshoot or undershoot eventually, the LED itself can flicker or produce other undesirable effects in the meantime as a result of the sporadic load current behavior.